Optical fibers have come into wide-spread use as transmission media for communication signals. Applications include video distribution systems, data and voice communications, and sensor signal networks. Both multimode and single mode optical fiber systems are employed for such purposes.
One of the limitations encountered by optical fiber systems relates to optical noise. A common source of optical noise is optical power reflections. Optical power reflection generally occurs at any discontinuity in a fiber optic transmission path, including the end of an optical fiber, and causes a portion of the incident light to travel back toward the source. Optical power reflected in this manner may reflect again when it arrives at the source point or other points of discontinuity in the system, adding an unwanted noise component to the signal. Optical power that is reflected back into a source can also corrupt the fundamental operation of the source, typically a laser. See for instance, R. Rao et al., Electronics Letters, Vol. 22 (14) pages 731-732 (1986), incorporated herein by reference. Control of reflections thus is an important consideration in the design of optical fiber systems.
It is known that reflections can be essentially eliminated if the fiber end is polished at an angle such that light is reflected at an angle beyond the internal critical angle of the fiber, thereby ensuring that the reflected light is not guided by the fiber. However, polishing typically is a time consuming operation that can considerably increase the cost of an optical fiber system. Another known technique for eliminating back reflection is to cleave the fiber such that a tilted end face results, as is described in Blonder, "Method of Producing Apparatus Comprising a Low Reflection Optical Fiber Connection," U.S. Pat. No. 5,048,908. However, special equipment is needed to perform this operation. Other disadvantages associated with current methods of terminating optical fiber include the possibility of sub-surface damage, fiber breakage and contamination.
Consequently, an apparatus having a low-reflection optical fiber termination which can be practiced easily, quickly and inexpensively, and that requires no additional or special equipment would be highly desirable. Ibis application discloses such an apparatus.
Various types of optical fiber connectors are known, including connectors which use index matching liquid to improve optical coupling between the fibers. An example of such a connector is described in, Runge, "Optical Fiber Connector", U.S. Pat. No. 4,512,630.